If you are a member of the Church of Jesus Christ of Latter-day Saints, you can link your FamilySearch account with a free Church of Jesus Christ-Ancestry account. Doing so will allow you to copy your ancestors from FamilySearch into a tree on Ancestry.com. More information here: https://partners.familysearch.org/solutionsgallery/s/gallery-profile/a2Rf10000079nvjEAA/00082
If you are not a member of the Church of Jesus Christ of Latter-day Saints, there is no way to directly copy your tree from FamilySearch Family Tree into an Ancestry tree. You will need to get a third-party program to convert between the two.
That said, the only software that I know of that syncs with both FamilySearch Family Tree and Ancestry.com trees is RootsMagic, but I believe that there are limitations on its ability to do so. You might want to watch some of the tutorials and videos to understand how to use it most effectively.